Poor, cute bunnies likely to get eaten when the snow melts early

Hares change coat color for winter based on the calendar, not the conditions.

Animals that turn white in winter are having a mismatch with the reduced snowpack in their environments.

Measuring the impact of climate change on animals is difficult, because (a) climate change is complex and (b) animals are complex. Climate change can alter the environment in many different ways, and each of these changes can affect the food supplies, hibernation patterns, reproductive behavior, and migratory patterns of different animal species. The changes in the animals all affect each other, too, since many of them are interrelated in food chains and webs that can be hard to disentangle.

Luckily, researchers at the University of Montana stumbled upon one simple, obvious part of an animal that they could measure in response to a simple, obvious change in climate. Snowshoe hares change color from brown to white in the winter so they can be camouflaged in the snow. So do at least nine other species of cute, cuddly mammals: Arctic foxes, collared lemmings, long-tailed weasels, stoats, mountain hares, Arctic hares, white-tailed jackrabbits, Siberian hamsters, and least weasels. (Bet you didn't know that hamsters are tough enough to handle winter in Siberia.)

Conveniently, the winters of 2010 and 2011 were the least snowy and snowiest winters, respectively, in the last 40 years at the authors' study site in western Montana. So the researchers asked: when there is less snow—and snow cover has generally been melting off earlier in winter—does that affect when the hares turn white?

They looked at 148 hares over the course of three years and compared how white the hares were to how much snow surrounded them. They found that the dates when the coat color molts started were fixed; the animals turned from brown to white in the fall and from white back to brown in the spring like clockwork. This was not surprising, since these dates are known to depend on the hares’ daily exposure to light.

But the rate of color change was fixed in the fall, not in the spring. The brown to white change took 40 days in each of the three years examined. In 2011, however, which had the longest snow season, the hares took 16 days longer to transition from white back to brown than they had in 2010. And just like in humans, girls matured faster than boys; female hares completed the spring molt 11 days before males.

According to their climate projections, the duration of snowpack in their area will be about a month shorter by midcentury and up to two months shorter by the end of the century. Predation already accounts for 85-100 percent of mortality in snowshoe hares. If the initiation dates of their molts don’t change accordingly—or if the lack of snow doesn’t also affect the Canada lynx that eats them—they might be in for a rough future.